1. Field of the Invention
The present invention relates to a technique of multicasting an email, and particularly relates to a technique of multicasting an email without causing congestion on a network.
2. Description of the Related Art
In recent years, a variety of techniques for supporting data communication using an email have been proposed. For example, Japanese Patent Application Laid-open Publication No. 09-51353 discloses an email server which changes the amount of data distributed as an email dynamically in accordance with the remaining amount of memory of a receiving terminal. The email server acquires information on the remaining amount of memory of a terminal device in advance, and before sending an email to the terminal device, compares the data amount of the email and the remaining amount of memory of the terminal device. If the latter is smaller, the email server divides the email at every breakpoint such as a punctuation and a period, and sends the divided emails sequentially. The terminal device, when receiving the divided emails, restores the original email by reconstructing the divided emails.
Japanese Patent Application Laid-open Publication No. 2002-207669 discloses a mail server which controls the data amount of an advertisement mail distributed by an advertiser. The mail server mediates an advertisement mail from an advertiser who is a sender of an advertisement mail to user terminals which are receivers of the advertisement mail. The mail server receives information on advertisement distribution conditions from each user terminal, and registers the information in its database. The mail server, when receiving from an advertiser an advertisement mail, adjusts the data amount of the advertisement mail for each user with reference to information on advertisement distribution conditions registered in the database, and distributes the advertisement mail to each user terminal.
However, the techniques disclosed in the above publications cannot solve a problem of congestion on a network which can be caused by multicasting of an email.
In recent years, an information service where information relating to a certain genre is sent as an email to multiple destinations has been known.
A server providing such an information service pre-registers the email addresses of users requesting an information service in its database, and if new information to be distributed is prepared, sends an email containing the information to the registered email addresses via nodes constituting the Internet and/or a mobile packet communication network.
In the information service, since a large number of emails are distributed in a relatively short time, if the destinations of the emails are concentrated in one area, an excessive load is applied to a network of the area, and thereby it is possible that congestion is caused on the network.
The present invention has been made in view of the above circumstances, and provides an email multicasting device which changes a distribution interval of emails dynamically in accordance with the number of emails to be multicast.